Cartoon backbone representation

Cartoon backbone representation is one way to represent a 3D protein structure that puts emphasis on secondary structure. Showing all of the atoms in a protein structure can be confusing due to the complexity of the structure, so backbone representations, like the cartoon backbone representation, simplify the picture by showing only a trace that connects the alpha-carbons in the structure. The cartoon backbone representation depicts alpha-helices using flat helical sheets and beta-sheets via flat level sheets, many times with arrows to indicate the N->C direction of the helices or sheets.

The structure on the right of a human transferrin n-lobe mutant (PDB code 1dtg) is shown in cartoon backbone representation with alpha-helices in magenta and beta-sheets in yellow.